Nuclear Theory·nucl-th

Friday·July 31, 2020

8 papers—2 primary·6 cross-listed

01
Far-from-equilibrium search for the QCD critical point
Travis Dore🇺🇸 · Emma McLaughlin🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸
Initial conditions for relativistic heavy-ion collisions may be far from equilibrium (i.e. there are large initial contributions from the shear stress tensor and bulk pressure) but it is expected that on very short time scales the dynamics converge to a universal attractor that defines hydrodynamic behavior. Thus far, studies of this nature have only considered an idealized situation at LHC energies (high temperatures $T$ and vanishing baryon chemical potential $μ_{B} = 0$ ) but, in this work, we investigate for the first time how far-from-equilibrium effects may influence experimentally driven searches for the Quantum Chromodynamic critical point at RHIC. We find that the path to the critical point is heavily influenced by far from equilibrium initial conditions where viscous effects lead to dramatically different ${T, μ_{B}}$ trajectories through the QCD phase diagram. We compare hydrodynamic equations of motion with shear and bulk coupled together at finite $μ_{B}$ for both DNMR and phenomenological Israel-Stewart equations of motion and discuss their influence on potential attractors at finite $μ_{B}$ and their corresponding ${T, μ_{B}}$ trajectories.
nucl-thPRD(2020)·71 citations
02
A Bayesian-Neural-Network Prediction for Fragment Production in Proton Induced Spallation Reaction
Chun-Wang Ma · Dan Peng · Hui-Ling Wei · Yu-Ting Wang · Jie Pu
Fragments productions in spallation reactions are key infrastructure data for various applications. Based on the empirical parameterizations {\sc spacs}, a Bayesian-neural-network (BNN) approach is established to predict the fragment cross sections in the proton induced spallation reactions. A systematic investigation have been performed for the measured proton induced spallation reactions of systems ranging from the intermediate to the heavy nuclei and the incident energy ranging from 168 MeV/u to 1500 MeV/u. By learning the residuals between the experimental measurements and the {\sc spacs} predictions, the BNN predicted results are in good agreement with the measured results. The established method is suggested to benefit the related researches in the nuclear astrophysics, nuclear radioactive beam source, accelerator driven systems, and proton therapy, etc.
nucl-thnucl-exCPC(2020)·17 citations
03
The LPM effect in sequential bremsstrahlung: nearly complete results for QCD
Peter Arnold🇺🇸 · Tyler Gorda🇺🇸 · Shahin Iqbal🇨🇳
The splitting processes of bremsstrahlung and pair production in a medium are coherent over large distances in the very high energy limit, which leads to a suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. We continue study of the case when the coherence lengths of two consecutive splitting processes overlap (which is important for understanding corrections to standard treatments of the LPM effect in QCD), avoiding soft-emission approximations. Previous work has computed overlap effects for double splitting $g \to g g \to g g g$ . To make use of those results, one also needs calculations of related virtual loop corrections to single splitting $g \to g g$ in order to cancel severe (power-law) infrared (IR) divergences. This paper provides calculations of nearly all such processes involving gluons and discusses how to organize the results to demonstrate the cancellation. In the soft emission limit, our results reproduce the known double-log behavior of earlier authors who worked in leading-log approximation. We also present a first (albeit numerical and not yet analytic) investigation of sub-leading, single IR logarithms. Ultraviolet divergences appearing in our calculations correctly renormalize the coupling $α_{s}$ in the usual LPM result for leading-order $g \to g g$ .
↳ hep-phnucl-thJHEP(2020)·46 citations
04
PDF in PDFs from Hadronic Tensor and LaMET
Keh-Fei Liu🇺🇸
We point out a problem of the phenomenological definition of the valence partons as the difference between the partons and antipartons in the context of the NNLO evolution equations. After demonstrating that the classification of the parton degrees of freedom (PDF) of the parton distribution functions (PDFs) are the same in the QCD path-intergral formulations of the hadronic tensor and the quasi-PDF with LaMET, we resolve the problem by showing that the proper definition of the valence should be in terms of those in the connected insertions only. We also prove that the strange partons appear as the disconnected sea in the nucleon.
↳ hep-phhep-latnucl-thPRD(2020)·23 citations
05
Parity-transfer $(^{16} O,^{16} F (0^{-}, g.s.))$ reaction as a selective probe of isovector $0^{-}$ states in nuclei
M. Dozono · M. Ichimura · S. Michimasa · M. Takaki · M. Kobayashi · M. Matsushita · S. Ota · H. Tokieda · N. Fukuda · N. Inabe · S. Kawase · K. Kisamori and 25 other authors
We demonstrate that the parity-transfer $(^{16} O,^{16} F (0^{-}, g.s.))$ reaction provides a selective probe of isovector $0^{-}$ excitations in nuclei. This reaction selectively populates unnatural-parity states through a $0^{+} \to 0^{-}$ transition in the projectile. The excitation-energy spectrum of $^{12} B$ was reconstructed via the $^{12} C (^{16} O,^{16} F (0^{-}, g.s.))$ reaction at 247~MeV/u from the coincident detection of the $^{15} O + p$ decay products of $^{16} F$ . The known $0^{-}$ state at $E_{x} = 9.3 MeV$ was clearly observed with an enhanced forward cross section, confirming the selectivity of the reaction. Structures observed at $E_{x} = 6.6 \pm 0.4$ and $14.8 \pm 0.3 MeV$ exhibit forward-peaked angular distributions and are suggested to contain significant $0^{-}$ strength. These results demonstrate that the parity-transfer reaction provides a powerful probe of $0^{-}$ excitations and highlight its potential for systematic studies of spin-isospin modes, including pion-related dynamics, in nuclei.
↳ nucl-exnucl-thPTEP(2026)·2 citations
06
Some Properties of the $QQq$ -Quark Potential in String Models
Oleg Andreev🇷🇺
We propose a string theory construction which allows us to study properties of the potential of two heavy quarks coupled to a light quark. In such a case, the potential is a function of separation between the heavy quarks. The results show the universality of the string tension and factorization at small separations expected from heavy quark-diquark symmetry. In addition, we make an estimate of the string breaking distance. With the parameter values we use, this distance is found to be almost the same as that for the heavy quark-antiquark potential. We also discuss the heavy quark-quark potential and its relation to Lipkin rule.
↳ hep-phhep-lathep-thnucl-thJHEP(2021)·17 citations
07
Two-neutrino double-beta decay in pionless effective field theory from a Euclidean finite-volume correlation function
Zohreh Davoudi🇺🇸 · Saurabh V. Kadam🇺🇸
Two-neutrino double-beta decay of certain nuclear isotopes is one of the rarest Standard Model processes observed in nature. Its neutrinoless counterpart is an exotic lepton-number nonconserving process that is widely searched for to determine if the neutrinos are Majorana fermions. In order to connect the rate of these processes to the Standard Model and beyond the Standard Model interactions, it is essential that the corresponding nuclear matrix elements are constrained reliably from theory. Lattice quantum chromodynamics (LQCD) and low-energy effective field theories (EFTs) are expected to play an essential role in constraining the matrix element of the two-nucleon subprocess, which could in turn provide the input into ab initio nuclear-structure calculations in larger isotopes. Focusing on the two-neutrino process $nn \to pp (ee ν ˉ_{e} ν ˉ_{e})$ , the amplitude is constructed in this work in pionless EFT at next-to-leading order, demonstrating the emergence of a renormalization-scale independent amplitude and the absence of any new low-energy constant at this order beyond those present in the single-weak process. Most importantly, it is shown how a LQCD four-point correlation function in Euclidean and finite-volume spacetime can be used to constrain the Minkowski infinite-volume amplitude in the EFT. The same formalism is provided for the related single-weak process, which is an input to the double- $β$ decay formalism. The LQCD-EFT matching procedure outlined for the double-weak amplitude paves the road toward constraining the two-nucleon matrix element entering the neutrinoless double-beta decay amplitude with a light Majorana neutrino.
↳ hep-lathep-phnucl-thPRD(2020)·23 citations
08
A quantum Monte Carlo based approach to intranuclear cascades
Joshua Isaacson🇺🇸 · William I. Jay🇺🇸 · Alessandro Lovato🇮🇹 · Pedro A. N. Machado🇺🇸 · Noemi Rocco🇺🇸
We propose a novel approach to intranuclear cascades which takes as input quantum MonteCarlo nuclear configurations and uses a semi-classical, impact-parameter based algorithm to modelthe propagation of protons and neutrons in the nuclear medium. We successfully compare oursimulations to available proton-carbon scattering data and nuclear-transparency measurements. Byanalyzing the dependence of the simulated observables upon the ingredients entering our intranuclearcascade algorithm, we provide a quantitative understanding of their impact. Particular emphasisis devoted to the role played by nuclear correlations, the Pauli exclusion principle, and interactionprobability distributions.
↳ hep-phhep-exnucl-thPRC(2021)·23 citations

Affiliations

first authorsco-authorsvia INSPIRE